This application claims the priority of Korean Patent Application No. 10-2003-0046976 filed on Jul. 10, 2003 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of Invention
The present invention relates to a method for efficiently updating an ARP (Address Resolution Protocol) cache table in an ad hoc network, and more particularly, to a method and system for dynamically updating information registered in the ARP cache tables of other terminals when an IP (Internet Protocol) address of a terminal existing in an ad hoc network changes due to collision with other IP addresses.
2. Description of the Related Art
According to FIG. 1 showing the related art, when a terminal 150 existing in an ad hoc network moves by itself or gets disconnected from the ad hoc network due to a certain condition, the terminal 150 has generally broadcast an Unsolicited Address Resolution Protocol (UnARP) packet. In response to the broadcast, each of neighboring terminals 110 to 140 looks up or examines its own ARP cache table and deletes the cached IP value of the terminal 150 when it is found to be present in its own cache table. Through such a procedure, existence of hosts having different MAC (Media Access Control) addresses can be prevented in the same IP address.
Since only general wired networks are considered in the related art, it is substantially difficult to detect which host gets disconnected from a network. Currently, only draft RFC (Request for Comments) is available. The RFC means official technical documents related to Internet technologies, which are released from IETF (Internet Engineering Task Force) and offers fundamental schemes for informing new ideas about research on and standards for protocols. The Information Science Institute in the University of Southern California in U.S.A. provides a list of all searchable RFCs released from IETF. Thus, more detailed contents on ARP can be obtained from the website “http://www.rfc-editor.org/rfc.html”. For example, RFC826 and RFC1868 include contents related to general ARP and UnARP, respectively.
In an ad hoc network, the IP address of a specific terminal may be changed, to avoid collision with IP addresses of terminals, and also when a terminal becomes disconnected from the network. Therefore, use of only UnARP leads to inefficiencies. Further, such a method cannot also provide solutions when packet loss occurs.
Since a MANet (Mobile Ad hoc Network) may be configured without help from any equipment such as an AP (Access Point) in the infrastructure, a protocol for assigning IP addresses, such as DHCP (Dynamic Host Configuration Protocol) used in a wired network, cannot be used. Therefore, it is necessary for a terminal to assign itself an IP address and to detect IP address duplication. However, in a MANet, duplicate IP address assignment may occur in the process of automatic IP address assignment. The ARP cache tables of the existing hosts remain unchanged when an IP address changes due to IP address collision, thereby causing a problem.
Even though the ARP cache tables are designed to be updated after a predetermined time period, normal communications cannot be made during the period because of incorrect ARP cache tables due to the change in IP address. The time period required for updating the ARP cache tables is not specified as a standard, but the time period is within a range of 2 minutes to 4 hours. Such an update scheme is configured in such a manner that each of the terminals broadcasts a request for the IP address and MAC address to the neighboring terminals and then the neighboring terminals transmit the desired address information in a unicast response.
If a method for reducing the update time period is employed to solve the above problem, a great deal of network resources is consumed accordingly. Thus, the method is not efficient. Therefore, there is needed a method of allowing normal communications to be made by dynamically updating the ARP cache tables when the IP address have been changed.